1. Field of the Invention
This invention relates to a device and a method for efficiently searching for a material capable of forming an interband phase difference soliton circuit that is one of the superconducting circuits.
2. Description of the Prior Art
The superconducting electronics that utilize the phase difference found among a plurality of superconducting components by using a multiband superconductor has been already known publicly (refer to JP-A 2003-209301 and JP-A 2005-085971, for example).
The bits to be used as basic elements of operation in these electronics are formed by utilizing an interband phase difference soliton (hereinafter referred to simply as “soliton”). The efficient generation of a soliton and the development of a method for the detection thereof are fundamental techniques for these electronics. Incidentally, the “soliton” used in the present invention has a feature of phase defect movable in a superconductor without accompanying any magnetic flux and, therefore, is to be distinguished from a fluxon.
For the sake of searching for materials that befit manufacturing circuits, available are (1) a method of search for a material, which comprises applying a DC, thereby generating a soliton between a superconductor and an electrode and determining the voltage generated by the extinction of the soliton with a voltage terminal and (2) a method of search for a material, which comprises determining fractional flux quantum generating in the superconductor loop due to a soliton (refer, for example, to the two prior art references mentioned above, “Soliton in Two-Band Superconductor,” Y. Tanaka, Physical Review Letters, Vol. 88, Number 1, Art. No. 017002 and “Interband Phase Modes and Nonequilibrium Soliton Structures in Two-Gap Superconductors,” A. Gurevich and W. M. Vinokur, Physical Review Letters, Vol. 90, Number 4, Art No. 047004).
In the technique utilizing the soliton as described above, a technique for manufacturing a material into a thin film, a technique for preparing a circuit and a technique for accurate determination of magnetic field and voltage have been found necessary.
Particularly, since the technique for determining magnetic field makes use of the principle that the flux quantum generated by the soliton assumes a halfway value, namely a value less than the ordinary flux quantum (2×10−7 gauss cm−2) (refer to “Soliton in Two-Band Superconductor,” Y. Tanaka, Physical Review Letters, Vol. 88, Number 1, Art. No. 017002), the request for this technique is serious. It is not easy to fulfill this request.
Further, the technique for manufacturing the electrode that is required by the technique for determining the voltage is not easy to attain. The multilayer high-temperature superconducting material, for example, that is a typical soliton candidate material is an oxide and generally necessitates use of gold as an electrode. It has been known that the establishment of ohmic contact between gold and an oxide material is not an easy thing (refer to “Low-resistivity contacts to the surface of superconductor thin films,” E. Harashima, N. A. Khan, Y. Sekita, K. Ishida, H. Ihara, SUPERCONDUCTOR SCIENCE & TECHNOLOGY 15 (1), pp. 29-31, January 2002).
This invention has been directed to the task of realizing a method for easy non-contact search for a material capable of generating a soliton without requiring a bulk material or a thin film material to be subjected to accurate determination of voltage or magnetic flux.